Ian Castles on Unsatisfactory Explanations & Climate Modelling

According to the ‘passionate claim’ introducing this thread [C02 Drives Climate: Svante Arrhenius], “we have no alternative to the enhanced greenhouse effect, we have no alternative theory of atmospheric radiation, we have no explanation of the warming based on physically credible models, and we have no basis to believe the greenhouse effect stopped functioning beyond 280ppm of CO2.”

The ‘sceptics’ are accordingly challenged to produce an alternative theory that explains the observed warming over the past century.

The argument is a powerful one if the prevailing consensus explanation does in fact offer a satisfactory explanation of what has happened. Several contributors have claimed that it does. They point to the conclusion in Meehl et al (2004) that “the late-twentieth-century warming can only be reproduced in the model if anthropogenic forcing (dominated by greenhouse gases) is included.”

ABW notes that this has “not been disputed in any peer reviewed journal”, and describes the paper as “very nice work.”

Coby provides a link to a Wikipedia entry with a graph and a table derived from Meehl et al at http://en.wikipedia.org/wiki/Image:Climate_Change_Attribution.png . These show, prima facie, that, “The temperature trend hindcasted over the last century matches observed temperatures very well, and this requires CO2’s radiative forcing.”

There is however a problem. According to the models, anthropogenic forcing is the net outcome of a positive forcing resulting from increasing atmospheric concentrations of greenhouse gaess (GHGs) and a negative forcing from emissions of sulphate aerosols.

The well-mixed GHGs presumably have a similar warming impact in both hemispheres, whereas the cooling effect of sulphate emissions should be concentrated in the northern hemisphere where 90% of such emissions are generated. This is explained, with illustrative maps, on the climateprediction.net website at http://www.climateprediction.net/science/s-cycle.php . The text states:

“The regions of high anthropogenic source emissions of sulphur dioxide leads to high concentrations of sulphate aerosol over the northern hemisphere continents. Unlike greenhouse gases, the distribution and concentration of sulphates varies a lot with location, as can be seen by comparing the sulphate concentration over the North Pole with that over North America.”

So if the prevailing explanation of warming is correct, the greater increase in temperature should be in the southern hemisphere. Yet between 1976 and 2000, according to the IPCC, the average decadal rise in the northern hemisphere was 0.24°C per decade, compared with 0.11°C per decade in the southern hemisphere: see Table II.2 at http://www.grida.no/climate/ipcc_tar/wg1/053.htm .
And according to the latest satellite records, as reported at http://vortex.nsstc.uah.edu/data/msu/t2lt/tltglhmam_5.2 , the difference between the two hemispheres is even greater. The average decadal rise from 1978 to the present was 0.200°C in the northern hemisphere, but in the southern hemisphere (where the increase should have been GREATER because of the much lower average levels of concentration of sulphate aerosols) the trend rise was 0.059°C per decade.

In the past fortnight, the mystery has deepened. In the wake of the discovery of a major error in one of the files being used in the BBC Climate Change Experiment, it was announced that models had been inputting greatly reduced levels of man-made sulphate emissions throughout their runtime. The consequence was “that aerosols responsible for “global dimming” (cooling) are not present in sufficient amounts and models have tended to warm up too quickly.”

The Principal Investigator of climateprediction.net, Myles Allen, said in a message to the participants in the experiment that, “In essence, what your models have done is show how much the world would have warmed up over the 20th century if it weren’t for the masking effect of global dimming.. “.

This was illustrated in a chart produced by one of the Oxford University researchers which showed that, for the average of 66 models that had ‘made it to at least 2005’, the global average temperature anomaly in that year was 1.9°C in the simulations, compared with a global average anomaly of only 0.5°C according to the real-world observations estimated by the Climate Research Unit (CRU) at the University of East Anglia. (The anomalies represent the temperature difference compared with 1941-50).

Thus the simulations suggest that the world would have warmed by no less than 1.9°C in the half-century or so to 2005, had it not been for the masking effect of sulphate aerosols. With these effects taken into account, the observed increase in mean temperature should have been only slightly less than this in the southern hemisphere, but much less in the northern hemisphere where almost all of the sulphate emissions are generated.

Yet in the real world, the opposite has occurred. All of the observations show that the average increase in temperatures was SMALLER in the southern hemisphere.

I don’t conclude that the greenhouse effect stopped functioning at 280 ppm, or that rising atmospheric concentrations of greenhouse gases don’t contribute to global warming, or that there is no need to be concerned about climate change.

I do conclude that the causes of climate change are not yet adequately understood (and may never be). It is not to the point that ‘sceptics’ haven’t produced an adequate explanation either, or that the Meehl et al paper hasn’t been disputed in any peer reviewed journal.

If the close correspondence between modelled results and observations that holds at the global level falls down at the broadest level of disaggregation (the two hemispheres), the explanatory power of the model must be seriously questioned. I would welcome comments on this heresy.

Funny stuff. Ian Castles makes an assumption about what climate models should do, without actually seeing if that is what climate models actually do, declares his unverified assumption puzzling and uses it to conclude that climate models are wrong. Only one problem – all his assumptions are wrong.

The basic mistake is to assume that hemispheric temperatures follow hemispheric forcings proportionately. This is incorrect. The biggest factor is the amount of oceans and the effective mixing depths in the southern oceans. This gives a much larger effective heat capacity in the south and so in any transient case the warming is always delayed in the south. This is actually exactly what climate models show.

Hi Gavin,
I would have thought you would be better off picking something that was checkable – if you want to learn.
Which I do, and which I think Ian C does.
So, when is it going to warm up in the southern hemisphere?
Are we going to be buffer by all the ocean here in Australia?
… I never read that in the CSIRO scenario modelling documents. My interest is particularly in rainfall, and they suggested we were going to feel it harder and sooner than anywhere else … or was that just a media release?

“I do conclude that the causes of climate change are not yet adequately understood (and may never be)…” … “by me” you forgot to add.

I have no problem with genuine scepticism. I have no problem with asking questions. I do have a problem with thinking of something, assuming it is a problem, assuming no one has an answer and concluding no one will ever know, all in one breathe.

Does it never occur to anyone that it is incredibly insulting to the people who have spent their lives trying to understand the climate? I see this on usenet’s sci.environment all the time. Someone thinks of the most elementary complication and because they have never done anyting but the most cursory research, they assume no one ever before has ever thought of it and triumphantly pronounces climate science as an ignorant religion. I think it is competely understandable that most climate scientists are not interested in responding to people who come with pre-formed conclusions that imply they are stupid or frauds.

It is a credit to people like Gavin that they understand the importance of this issue and therefore the importance of overlooking, for the most part, such egregious behaviour. But nevertheless, the primary consequence is that the real experts in general decide not to waste their time with prejudice matched by ignorance and it falls on non-experts like me to spend the time.

This necessarily results in worse communication because I will make more mistakes and not have as many answers.

My answer to you would have been, it is not so simple as you are assuming and the complications are the disproportionate amounts of land in the N hemisphere versus the S hemisphere, the ocean dynamics that are very different in the arctic versus the antarctic and the polar amplification that is both predicted and observed in the arctic. I don’t know the details.

It is a well-established rule of statutory interpretation that where legislation is ambiguous it should if possible be construed compatibly with treaties executed by the government.

As ratified treaties bind Australia in international law, Parliament has little choice but to enact implementing legislation, since Australia would otherwise be in breach of its international obligations.

It therefore matters not what climate science can or cannot predict. As a signatory state to Agenda 21, Australia is bound by the precautionary principle, which specfies that the lack of full scientific certainty should not be used as a reason for postponing measures to prevent environmental degradation.

Its basis for action, objectives, activities and means of implementation may be found in AGENDA 21, SECTION 2, CONSERVATION AND MANAGEMENT OF RESOURCES FOR DEVELOPMENT, Protection of the atmosphere 9.1 – 9.35.

“I am sure this is a stupid question for the scientists who post here, but I am new to this: do aerosols, especially the dark ones, have an insulating effect for the lower atmosphere therefore increasing the amount of heat trapped there while reflecting sunlight from the upper atmosphere?

[Response: There is nothing obvious about aerosol effects, so no questions are stupid! Reflective aerosols (sulfates, nitrates) cause light to scatter back out to space and so have a cooling effect, but they also absorb a little and casue a local warming (this happens with volcanic aerosols as well). The dark ones (basically soot) absorb more and darken the earth relative to what it was and so end up warming the planet. Aerosols also have effects in the long-wave and interact with clouds and chemistry so the net effects are pretty complicated – hence the uncertainty in assessing their forcing. – gavin]

Comment by ocean — 17 Apr 2006 @ 6:54 pm
#

A little more explanation of these different effects of aerosols would be helpful: “light scattering sulfate aerosols, light absorbing carbonaceous aerosols like soot and even aerosol effects on cloud properties (indirect aerosol effects).”

Are you suggesting I should just throw my hands in the air and my fridges out the window and not think about the implications of global warming or, for example, why temperatures have only risen 0.6C globally over the last 30 years despite the significant increase in carbon dioxide?

One of my problems is that I am expected to know something about water and the impression everyone has, based on CSIRO publicity, is that its going to get a lot drier here in Australia.
Now extrapolating from Gavin’s response to Ian – is it possible that with all the ocean and all the heating it could get a lot wetter in Australia?

While Cody may be annoyed by questions, there is in my view nothing more important, than the capacity for interested and thinking individuals to be able to ask questions. And I am curious that they are met with such distain by the established experts – particularly given what they are expecting us to believe.

Who’s read Stephen Jay Gould and The Rocks of AGes: Science and Religon in the Fullness of Life?

Not at all, Jennifer. What I’m suggesting is that the environmental objective of protecting earth’s atmosphere from human-induced degradation has already been identified. Also, Australia has already undertaken to implement solutions to this identified problem through its international obligations as defined within Agenda 21.

The sheer magnitude of this global ideological toing and froing allows contrarian interests to peddle their own versions of gloom and doom, but fourteen years have now elapsed since Australia obligated itself in Rio de Janeiro in June, 1992.

“I do have a problem with thinking of
something, assuming it is a problem, assuming
no one has an answer and concluding no one
will ever know, all in one breathe.”

By all means ask the questions. But why oh why don’t you wait to see what the answer is?? I *really* want to know!!

As for precipitation and Australia, your impression of the overall general correlation between warmth and precipitation is, I believe, correct. However, Australia is projected to dry. I do not know why. Probably just need to pay the modeler a bit more and you can get the projection you’d like, right?

“why temperatures have only risen 0.6C globally
over the last 30 years despite the significant
increase in carbon dioxide?”

Firstly, that really is an awful lot in a short time. NOAA has this opinion about the last 1000 years: “warming was most dramatic after 1920″. Please note this does not mean there was more dramatic warming before 1000 years ago it only means there is less known. 1970’s to today was the most dramatic part of that drama as well.

The other thing to understand is that due to very large thermal inertia there is a lag of several decades between the application of a radiative forcing and the final new equilibrium temperature. IOW, if CO2 levels stopped right where they are today, we would still see a few decades of warming.

“why temperatures have only risen 0.6C globally
over the last 30 years despite the significant
increase in carbon dioxide?”

Firstly, that really is an awful lot in a short time. NOAA has this opinion about the last 1000 years: “warming was most dramatic after 1920″. Please note this does not mean there was more dramatic warming before 1000 years ago it only means there is less known. 1970’s to today was the most dramatic part of that drama as well.

The other thing to understand is that due to very large thermal inertia there is a lag of several decades between the application of a radiative forcing and the final new equilibrium temperature. IOW, if CO2 levels stopped right where they are today, we would still see a few decades of warming.

Thanks Gavin for providing a link to the GISS Model E study (Hansen et al, December 2005). Dr. Hansen had in fact sent me the abstract of the paper, and a link to the full text, on 28 December 2005 – with the notation ‘Criticisms would be welcomed’. I was also advised of the journal to which the paper had been submitted.

I admire the wealth of detail provided in GISS paper and databases, and the frank admission of uncertainties. In fact, I would have thought that my conclusion that ‘the causes of climate change are not YET adequately understood (and MAY never be)’ (EMPHASES added) receives considerable support in some of the discussion in this paper: see, in particular, Section 2.4 (‘Principal model deficiencies’).

I have frequently cited the GISS estimates and projections in contributions to this website, and also used them extensively in my paper for ‘Online Opinion’ (‘The Role of the IPCC is to Assess Climate change not Advocate Kyoto http://www.onlineopinion.com.au/view.asp?article=2147’).

I have no problem in acknowledging that much of the paper is beyond my area of expertise, particularly as it is only too apparent that some of the matters upon which the 46 authors pronounce with such authority ARE within my area of expertise and are outside theirs’.

For example, there are repeated references to the IPCC A1FI, A2 and A1B scenarios as ‘business as usual’ or ‘BAU’ scenarios (see pps. 27 and 32 in particular), even though the authors of the IPCC Special Report on Emission Scenarios (SRES) themselves stated that ‘There is no “business-as-usual” scenario’ (Technical Summary, s. 6, p. 27) and that they regard scenarios of a long-term closure of the North-South income gap as ‘highly unlikely’ (Nakicenovic et al, E&E, 14, 2&3: 196). Yet you and your 45 co-authors continue to treat these scenarios as ‘business as usual’.

It is true as the paper says that current CO2 emission trends fail to meet the GISS Alternative Scenario, but I believe that this conclusion relies excessively on the relatively high increases in 2003 and 2004.

Could I suggest that you and your colleagues study the projections of CO2 emissions from fuel combustion to 2030 in the Reference and the Alternative Scenarios of the International Energy Agency, as published in ‘World Energy Outlook 2004’, and the somewhat reduced projections for 2030 in the IEA Reference Scenario as published in ‘World Energy Outlook 2005’. CO2 Emissions in the IEA Alternative Scenario for 2030 (which are based on assumptions carefully stated in the publication) are virtually identical to the IPCC B1T MESSAGE scenario.

These IEA projections draw on a mass of information on countries’ policies, investment plans of energy authorities, etc. and I find it surprising that they seem to be ignored by the climate science community.

It is the B1T message scenario (not the B1 marker scenario cited in your paper) which has the lowest forcing of the IPCC emissions scenarios. For a comparison of this scenario’s projected temperature increases with the ‘Hansen’ scenarios, see the chart on p. 2 of no. 2 of the Australian Greenhouse Office’s ‘Hot Topics in Climate Change Science: the link is at http://www.greenhouse.gov.au/science/hottopics/index.html . This chart shows how highly misleading the Hansen et al paper is in referring to the scenarios based on the IPCC’s more imaginative ‘storylines’ as ‘business-as-usual’.

The Hansen et al paper states that ‘Global aerosol distributions are computed with the transport model for .. 1990 AND KEPT CONSTANT AFTER 1990’ (EMPHASES added). Please refer to the chart at http://www.climateprediction.net/board/viewtopic.php?p=42756#42756 , which shows that by far the greatest part of the extremely rapid increase in the ‘without aerosols’ results from the aborted climateprediction.net experiment occurred between 1990 and 2005.

As changes in global aerosol distribution are excluded by assumption in your paper, I think your dismissal of my suggestion that the close correspondence between modelled results and observations breaks down at the hemispheric level may be premature.

In any case I am glad that I invited comments, because this has resulted in the Hansen et al paper being considered here. I would certainly be interested in any comments that Australia’s Warwick McKibbin might have on the concluding sections of the paper.

With regard to Jennifer’s comments on prospective rainfall in the Australian context, and the message currently reaching the Australian public that ‘greenhouse’ is associated with a ‘brownhouse’ (as noted by Roderick, Farquhar & Rotstayn at the Greenhouse 2005 conference) the Hansen et al paper states that ‘Well-mixed GHGs by themselves are simulated to yield large increases in global precipitation and run–off.. A tendency for these changes remains when all forcings are applied’ (p. 20).

Finally, I note from the listing of affiliations at the head of the paper that several co-authors (including yourself) are affiliated with Columbia University. I urge you to use any influence you may have in that institution to secure the removal of the database of downscaled GDP estimates at http://beta.ciesin.columbia.edu/datasets/downscaled/ .

I warned in my presentation to the IPCC Expert Meeting in Amsterdam in January 2003 of the risk ‘that the dissemination of this material will be worse than useless: it will encourage researchers to base their work on faulty data and to reach unsound conclusions.’ Regrettably my concerns were ignored, and I have no doubt that many of the impact and vulnerability studies that will be cited in the WGII contribution to AR4 will be seriously flawed as a result.

Incredibly, the ‘guidance paper’ which is published on the downscaled data website at CIESIN survived peer review, and was published in the journal ‘Global Environmental Change’ (then edited by IPCC WGII Co-Chair Martin Parry) in July 2004.

According to the abstract of this paper, ‘we also generated geo-spatial grids at 1/4° resolution (30 km at the equator) for.. GDP “density” (GDP/unit land area) for two time slices, 1990 and 2025.’ These absurd maps showing the ‘market exchange rate density’ of world GDP (p. 52 of the guidance paper) were reproduced in the final version of the paper as published in GEC. The first-named author of the paper was a Lead Author of the SRES and one of the other authors is a Coordinating Lead Author of Chapter I of the WGII Contribution to AR4.

The paper accuses David Henderson and me of having created ‘confusion and misinformation’, and says that ‘Recent replies by the SRES lead authors have sought to correct the misinformation.’ One of the two references cited in support of this claim is ‘Nakicenovic, N., et al., 2003b. Emissions scenarios and the work of the IPCC: a final response to Drs Castles and Henderson. Energy and Environment 14 (4)’. No such paper has been published, although it is possible that the reference cited by Gaffin et al was an unpublished draft of a paper that subsequently appeared by a different first-named author (Grubler), in a different year (2004) and with a title that did not mention ‘Drs Castles and Henderson’ (neither of us is a ‘Dr’, incidentally).

Coby asks whether it ever occurs to anyone that [the points that I have raised are] incredibly insulting to the people who have spent their lives trying to understand the climate? Has it ever occurred to him how incredibly insulting to economists and national accounts statisticians it is that the IPCC persists with discredited statistical concepts and undermines the efforts to measure output that they have developed over the past 60 years.

And that Columbia University accepts funding from NASA to produce databases that make no positive contribution to knowledge and lead render useless a large volume of research effort that relies upon erroneous data?

When the Goulburn dam was recently declared empty, a nearby farmer who had family records for over a century said on television that going on past experience, the drought could last another seven years.

The CSIRO does not model that australia will uniformly have less rainfall, and, to my knowledge, they do not put in their media releases that global warming = less rainfall always across australia.

Jennifer could you provide a link to a CSIRO media release where they say that rainfall will decrease across australia?

I’m sure they have said ‘drier’, but i do not think this disagrees with their modelling.

CSIRO look at both rainfall changes (rainfall is projected to vary, sometimes increases, sometimes decreases, and difficult to judge across the continent) and evaporation changes (projected to almost uniformly increase across the continent). They conclude that overall moisture balance will deteriorate across most of the continent, ie it will be drier.

“Evaporation and moisture balance:
Warmer conditions will lead to increased evaporation. When this is combined with the simulated changes in rainfall, there is a decrease in available moisture. This means greater moisture stress for Australia.”

Coby, You say, in criticism of me, that you have a problem with someone ‘thinking of something, assuming it is a problem, assuming no one has an answer and concluding no one will ever know, all in one breath.’

Let me first comment on the ‘no one will ever know’ part. I’ve already pointed out that that was not what I said. But let me remind you of what the IPCC said (as quoted in a submission by nine economists, including me, on the Stern Review discussion papers):

‘In climate research and modelling, we should recognise that we are dealing with a coupled non-linear chaotic system, and therefore that the long-term prediction of future climate states is not possible. The most we can expect to achieve is the prediction of the probability distribution of the system’s future possible states by the generation of ensembles of model solutions’ (IPCC TAR, 2001, Report of WGI, p. 774).

In charging that I simultaneously thought of something, assumed it is a problem and assumed that no one has an answer, I suggest that you were yourself making some rather bold assumptions about my mental processes.

If you go to http://www.climateprediction.net/science/s-cycle.php , you will find a representation of the globe that shows ‘one model’s surface temperature response to increasing sulphur emissions from pre-industrial levels (natural) to PRESENT DAY levels (natural plus anthropogenic).’ (EMPHASIS added).

The climateprediction.net scientists who produced this map explain that ‘The cooling effect of sulphate aerosol can be seen throughout the whole northern hemisphere and corresponds to the high sulphate burden of the northern hemisphere shown in Figure 2.’

I emphasise that this map does NOT show the geographical distribution of relative sulphate burdens: it shows the modelled estimates of ‘the cooling effect of sulphate aerosols’ (measured on a scale from –0.3 C to +0.2 C). And they are striking: large areas of the northern hemisphere are coloured deep blue (minus 2.0 –3.0 C) and even larger areas are coloured a lighter blue (minus 1.0 -2.0 C).

Gavin said that I made the ‘basic mistake’ of assuming ‘that hemispheric temperatures follow hemispheric forcings proportionately. Well actually I didn’t assume that when these scientists used the word ‘corresponds’ they meant that the matching was precise. But yes I did assume that it is a problem that the hemisphere that has experienced much greater MODELLED COOLING effects is also the hemisphere that has experienced much greater OBSERVED WARMING.

And I didn’t ASSUME that no one has any resolution to this striking prima facie contradiction: on the contrary, I said that I ‘would welcome comments on this heresy.’

Despite my unhappy experiences in dealing with the IPCC milieu in recent years, I was really hoping for some civil comments and perhaps even an explanation. So far I’ve been disappointed – and I continue to be surprised at the extraordinary hypersensitivity to criticism of many climate scientists.

Correction. I said that the map on the climateprediction.net weebsite showed the modelled cooling effect of sulphate aerosols on a scale from –0.3 C to +0.2 C. The scale actually runs from minus 3.0 C to plus 2.0 C.

The reason I made the error is that when I first looked at the map I assumed that the extremes of the range of modelled effects would be 0.5 C. It was only when I studied the map more closely that I realised that the extremes were an order of magnitude greater. The results seem to me to be extraordinary.

I most recently became interested in the global warming issue because of the rhetoric that the IPCC used to dismiss the Henderson and Castles critique. Amongst other things they described this eminent pair as being “so-called” experts. Resort to unjustified ad-hominem attacks is a sure sign of a weak argument.

The response to Ian Castles’ comments in this post suggests that there is a real problem with the climate models in terms of where the warming is occurring. Merely saying that differential warming has been taken into account in climate models doesn’t constitute an adequate rebuttal.

Instead of references to arcane and difficult to translate papers I’d like to see some elementary mathematics. In my experience, if you can’t explain it in simple terms to the sort of extremely intelligent laymen who inhabit a blog like this, you’re probably talking nonsense.

“Coby asks whether it ever occurs to anyone that [the points that I have
raised are] incredibly insulting to the people who have spent their lives
trying to understand the climate?”

That is not correct, I don’t think I need to expain how. Your other complaint was about this:

“Coby, You say, in criticism of me, that you have a problem with someone
‘thinking of something, assuming it is a problem, assuming no one has an
answer and concluding no one will ever know, all in one breath.'”

Mea culpa for the exageration. I have that problem with many psuedo-objections that are raised and echoed around the internet. For the post under discussion I took a look at the climateprediction link you point to and will accept that you did not just assume there was a problem, you did try to check into it. So I will try again, in a different tone from the top.

Ian, you said “there is a problem” and set it up as follows:

1. the models predict warming as GHG positive forcings dominating aerosol
negative forcings.
2. well mixed GHG’s “presumably have a similar warming impact in both hemispheres”
3. cooling aerosol effects should show mostly in the NH “where 90% of such
emissions are generated”
– you offer http://www.climateprediction.net/science/s-cycle.php as support
4. You deduce from the above that “the greater increase in temperature should
be in the southern hemisphere”
5. You note this has not happened and conclude “the causes of climate change
are not yet adequately understood (and may never be).”

I hope I have not removed any essential element from your argument because this simplification shoud enable us to easily see where you have gone wrong. Point 2 is incorrect. It is realy that simple and it invalidates your conclusion. GHG warming is not expected to have similar warming in both hemispheres, you can see what the models do expect together with the observations (which they match quite well) in the paper that Gavin offered in comment #1. The reason is disproportionate amounts of ocean in the two hemispheres and that warming over land is greater. There is also a polar amplification effect expected and observed in the Arctic. Differing ocean dynamics contribute as well. These factors may or may not dominate in the order I have presented them.

You may be misinterpreting the mappings of aerosols and their effects in that link. It is ONLY showing the aerosol effect, it is not showing GHG minus aerosols. So, yes, aerosols cause significant cooling in the NH but this does not tell you the sum of all forcings. There are some interesting things to note in that image: cooling in general is greater over the oceans and aerosols cause additional warming in some places (just to further point out the dangers of oversimplifying).

To reiterate: there is no significant discrepancy between modeled and observed behaviours. I really think that should lay this issue to rest.

Graham – “Instead of references to arcane and difficult to translate papers I’d like to see some elementary mathematics. In my experience, if you can’t explain it in simple terms to the sort of extremely intelligent laymen who inhabit a blog like this, you’re probably talking nonsense.”

As a layperson I understood it OK. It essentially is that the southern hemisphere has more water to heat up so it is warming slower than the northern hemisphere. Also the effect of aerosols is not simple as they both cut down on the amount of sun reaching the earth and also insulate as well. Sorting out the forcings is not easy. The GCMs in general sort it out pretty well however much work remains to be done.

Coby, I accept that I should not have said that well mixed GHGs “presumably have a similar warming impact in both hemispheres” (Figure 11 of Hansen et al, third map down in right column refers).

But I don’t agree that ‘there is no significant discrepancy between modeled and observed behaviours.’ For example, on my reading of Figure 18 of Hansen et al (2005), to which Gavin directed me, the observed warming exceeded modelled warming by a significant margin over much the greater part of the northern hemisphere in the 1979-2003 period. In the Antarctic the discrepancy was in the opposite direction.

For the world as a whole, both the observed and the modelled warming in this period was about 0.4°C – i.e., equivalent to less than one-seventh of the vertical axis of the Figure. Visual inspection suggests that, over about one-half of the globe, the DIFFERENCE between the observed and modelled warming for this 24-year period was similar to, or greater than, the observed average warming for the world as a whole for this period. I’m surprised that you think that these aren’t significant discrepancies.

I did not misinterpret the mapping of aerosols and their effects on the ‘Sulphur Cycle Experiment’ page of the climateprediction.net website. The description is quite clear: the map shows ‘the model’s surface temperature response to increasing sulphur emissions from pre-industrial levels.. to present day levels..’. The description also says that ‘The cooling effect of sulphate aerosol can be seen throughout the whole northern hemisphere’ (which isn’t strictly true: there is a warming effect in Northern Scandinavia).

The accompanying text says that ‘a PREDICTION of the climate of the 21st century needs to contain the effects of sulphate aerosol otherwise the warming trend may be OVERestimated’ (EMPHASES added). There are two errors here. First, the climateprediction.net simulations aren’t predictions; and secondly, the statement assumes, contrary to most expectations, that sulphate aerosol emissions will increase in the 21st century.

In fact, nearly all of scenarios project that emissions of sulphur oxides will DECREASE in this century. For the four SRES markers, the projected decreases between 2000 and 2100 are: A1, 60%; A2, 13%; B1, 84%; and B2, 31%. For the two illustrative A1 scenarios, the projected decreases are: A1FI, 42%; and A1T, 71%. These decreases lead to significant positive (negative of a negative) forcing in the 21st century, and concomitant WARMING in the IPCC scenarios.

There are huge uncertainties in relation to aerosols, both in respect of the trends in emissions in recent times and in the effects on climate. Having already tripped myself up once in a confusion of forcings and temperatures, I’ll avoid drawing my own conclusions and will simply draw a contrast between what Hansen et al (2005) say and what is posted on the climateprediction.net website:

(a) Hansen et al (2005) assess the total 1880-2003 negative aerosol forcing, including the indirect effect, as equivalent to more than one-half of the effective forcing for the total of the well-mixed GHGs (CO2, CH4, N2O and the CFCs) over the same period (pps. 5, 7). But they say that ‘empirical data for checking model-based temporal changes of tropospheric aerosol amount.. are meager’, and ‘Our largely subjective estimate of the uncertainty in the net aerosol forcing is at least 50%’ (p. 7).

(b) Hansen et al (2005) also say that: ‘Observed global warming, as well as the global warming in the model driven by all forcings, has been nearly constant at almost 0.15°C/decade over the past 3-4 decades, except for temporary interruptions by large volcanoes. This high warming rate has been maintained in the recent decade despite a slowdown in the growth rate of climate forcing by well-mixed GHGs.. The warming rate in the model is maintained because, BY ASSUMPTION, TROPOSPHERIC AEROSOLS STOP INCREASING IN 1990.. The ASSUMPTION that global aerosol amount approximately levelled off after 1990 IS UNCERTAIN, because adequate aerosol observations are not available.. An implicit well-known conclusion is that future global warming may depend substantially on how the global aerosol amount continues to evolve, as well as on the GHG growth rate’ (EMPHASES added).

(c) By (apparent) contrast, the simulations on the climateprediction.net website for the average of 66 models that had ‘made it to at least 2005’, to which I referred in an earlier post on this thread, show ‘overheating’ as a result of the non-inclusion of sulphate aerosols on what seems to be a much larger scale than implied in Hansen et al. Moreover, the widening of the gap between the ‘without aerosols’ temperature simulations and observations appears to be at least as great between 1990 and 2005 as in the decades preceding 1990.

To me, this suggests that the climateprediction.net estimates of aerosol emissions do NOT level off after 1990, and that a continuing growth in such emissions is reflected in the ‘Sulphur Cycle Experiment’ map.

In your initial post, Coby, you told me that for my follow up questions I might find Chapter 12 of the TAR informative, and provided a link. I am in fact quite familiar with what is said in that Chapter on regional climate projections, for which Australia’s John Zillman was Review Editor. If this post was not already overlong, I’d draw on the conclusions of that chapter, and on some of John’s subsequent statements on this subject, to reinforce some of the points made above.

I’m sorry if you think that I am again raising ‘the most elementary complication’ and that, because I ‘have never done anything but the most cursory research, [I] assume no one ever before has ever thought of it’ – and am ‘triumphantly pronounc[ing] climate science as an ignorant religion.’

You alleged, referring to me, ‘that it was completely understandable that most climate scientists are not interested in responding to people who come with pre-formed conclusions that imply they are stupid or frauds’, and said that it is ‘a credit to people like Gavin that they understand the importance of this issue and therefore the importance of overlooking, for the most part, such egregious behaviour.’

And you concluded that ‘the primary consequence is that the real experts in general decide not to waste their time with prejudice matched by ignorance and it falls on non-experts like [you] to spend the time.’

Let me assure you that I don’t come to climate change science issues with pre-formed conclusions that imply that climate change scientists are stupid or frauds. I tried for a long time to stick to my knitting, but found that I was being criticised (notably on this blog) for pleading ignorance of climate change science.

I’ve therefore decided that we should all be prepared to ask some dumb questions in areas outside our area of specialisation and that’s what I’m doing. I’ll have some separate questions to address to Gavin, but in the meantime I hope that you are able to take some time to respond to the issues raised above.

Ian, I have to apologize for my initial tone with you, and confess I mistook most of the post as Jennifer’s words rather than it being all yours. You do strike me as more serious minded about the science in this issue than she, I was therefore a bit too abrasive. Who knows, maybe I don’t give Jennifer enough credit, time will tell.

I can’t really add anything to your excerpts from Hansen’s papers, I hope the point is not to prove there are in fact uncertainties because that is a given. As for regional failures of modeled climate, the question of its significance is necessarily a judgement call. After all, to quote someone (?) “all models are wrong, but some are useful”. The failings you point out might lead one to say things are turning out worse than we would have expected, getting more warming where people live and less in the antarctic where it doesn’t matter.

You quoted climateprediction.net:
“a PREDICTION of the climate of the 21st century
needs to contain the effects of sulphate aerosol
otherwise the warming trend may be OVERestimated”

I agree they should use the word projected. I don’t see how this implies aerosols will increase, though have no knowledge of what they do assume. I really can’t say for sure if your inference from roughly equal widening of the non-aerosol vs observations gap in the 1990’s really means they are not using an aerosol scenario that levels off in the nineties. The effects may not be so linear.

I do appreciate the obvious time and effort that you are investing here. There are no dumb questions, only dumb answers. I will do my best to pass on what I know and provide resources where I can for what I don’t.

Archives

About Me

Jennifer Marohasy is a scientist, author and speaker.
Dr Marohasy has a PhD from the University of Queensland, worked for twelve years as a researcher for the Queensland government, then six years as environmental manager for the Queensland sugar industry, and then six years as a senior fellow at the Melbourne-based Institute of Public Affairs. She is currently an adjunct Research Fellow at Central Queensland University funded by the B. Macfie Family Foundation.
Read more

Subscribe For News Updates

First Name*

Last Name*

Email*

Name

This field is for validation purposes and should be left unchanged.

Contact Me

To get in touch with Jennifer call 0418873222 or international call +61418873222.